Add failing bounds checks for views

See #25
Bounds check the `len` of a Cstruct in the BE/LE modules.

Closes #25
Document that the `Cstruct.LE/BE` functions can raise `Invalid_argument`

Noted missing by @dbuenzli
Sync CHANGES and bump to 1.3.0 working version
Fix a vitypo
fix docstrings to use `@raise` and fix exception names

Suggested by @dbuenzli
Merge pull request #26 from avsm/more-bounds-on-views

More bounds on views